Problem description:
Well, what I basicly want is, when a player logs out and logs in again, the skills that they placed on the hotbar and logged out with, are still on the hotbar in the exact same position. So basicly a savesystem for this. But I wasn't able to figure it out myself. Can anyone help me?

You would save the location of each skill in a savefile and then read it back from the savefile when the player logs in. Using the information you saved, you then determine where to put them on the hot bar.

This worked for me, though you may want to overwrite empty buffers, as the skill stays there even if it was removed unless overwritten with null. Also note that it only works on a bottom row hotbar used via HUD. A similar principle could be used on any edge of the map by simply adjusting the buffer names.

The buffers/sub-directories(The things inside [] in F["[I],1"]) don't automatically delete when saving a new file, because you aren't overwriting them with anything. This means that if you remove a skill from the hotbar, then save with this system, it will pop back up when you load.

It's not incredibly difficult to counteract, you could add them to a list instead of individual buffers then put the list in a temp list during loading, then again to save to a single buffer/sub-directory. I chose not to to make the code less copy-pasteable, the concept is shown and you should be able to handle it from here.

This is a pretty poor way of saving well, anything. You're limiting the open-endedness of system and preventing it from being easily expanded in the future. What the original poster should be doing is keeping track of the skills on their own instead of relying on client.screen.

This is just an EXAMPLE, not hand-fed code, so you're meant to learn from it not use it. When the hotbar list is loaded, anything that was saved inside of it gets loaded as well, this includes all variables and whatnot, it will also call New() for the objects inside of it, which will add them to the player's screen. screen_loc is automatically saved with the object when you save the list, and should be loaded when the list gets loaded.